Carpet tiles are backed typically either with a thick layer of a bitumen or a polyvinyl chloride (PVC) backing composition. Bitumen-backed carpet tiles, due to the more thermoplastic nature of the backing layer, typically must be printed in large, slab form, rather than in individual tile forms as PVC, and then cut into individual tiles. Generally, carpet tiles are printed to a desired design on the fibrous face by employing a wet printing process which includes the application of aqueous dye and thickener onto the fibrous face with color fasteners and then the steaming, for example, for 3-10 minutes, of the carpet tile at live steam temperatures of 212.degree. F. to 220.degree. F. to fix the dye. Bitumen-backed carpet tiles when subjected to a wet printing process and live steam temperatures tend to have the face portion, that is, the fibrous face and the primary backing sheet, slide in relationship to the thermoplastic bitumen backing layer so that the resulting carpet tile edges after a wet printing process are uneven and exposed due to the instability at the higher temperatures of the bitumen backing layer. In addition and even if the carpet tile edges are not uneven, distorted or exposed, often the carpet tile develops rounded edges and/or curled edges. Therefore, bitumen-backed carpet tiles are generally printed in a wet printing process in slab form to reduce the problems arising from live steam or elevated temperature wet printing processes.
Bitumen compositions employed as carpet tile backing compositions usually include natural or synthetic bitumen and filler materials, such as calcium carbonate particles, and also modifying agents to impart desirable flexibility and stability properties to the bitumen composition. For example, bitumen backing compositions useful as a carpet tile backing layer and containing modifying polymers are described in U.S. Pat. No. 4,201,812, issued May 6, 1980, wherein a thermoplastic, styrene-butadiene-styrene block copolymer (SBS) is added to a low asphaltene bitumen to provide a carpet backing of defined flexibility and penetration values. However, the SBS modified bitumen carpet backing composition does not provide a carpet tile which may be printed in a steam, wet printing process without the problems associated therewith.
It has been suggested that carpets be backed with thixotropic polyurethane adhesives (see for example U.S. Pat. No. 3,895,149, issued July 15, 1975 hereby incorporated by reference in its entirety); however, such polyurethane-backed carpets are not commercially available, although a hydroxyl-terminated polybutadiene reacted with a polyisocyanate has been suggested as a composition as either a laminating adhesive, a precoat adhesive or as a unitary backing to the other side of a primary backing sheet of a tufted carpet in said patent.
Liquid hydroxyl-terminated homopolymers of polybutadiene, and the use of such homopolymers in isocyanate curing reactions to produce urethane polymers are commercially available, for example, as R-45M and R-45HT (poly BD) from Atochem, Inc. of The Elf Aquitaine Group. The hydroxyl-terminated polybutadiene homopolymers have been suggested for use in preparing either one step or two step, that is prepolymer, intermediate urethane polymers, and such urethane polymers have been suggested as extenders to be used with asphalt and as modifying additions to asphalt in the construction field to provide flexibility and durability to asphalt compositions employed in road construction and gravel and soil stabilization.
It is desirable to provide an improved, printable, bitumen-backed carpet tile and a method of producing a heat stable bitumen carpet tile particularly which may be employed in a wet, steam printing process without the disadvantages of the prior art bitumen-backed carpet tiles.